The Dead Man Running star mixed with alien-spotters when he investigated extra-terrestrials for his upcoming U.K. programme I Believe - but got a little too close to the subject matter for comfort.
He says, "I saw one, yeah. People think I'm a complete lunatic now but I did see something a bit mad. I went to America, to a hippie commune and had to get a bit spiritual... I went to meet some people who have been abducted and things like that, and they told me some really mad things. I think you have got to open your mind a little bit.
"I just want to believe that there's things (sic) out there. I did see something. It wasn't a plane, it wasn't a helicopter, it just looked like a massive star going across the sky. But it freaked me right out."
The Disney hit - starring Jim Carrey as an animated Ebenezer Scrooge - toppled Michael Jackson's This Is It from the top spot.
The documentary secured second place with $14 million (£8.75 million), followed by George Clooney's The Men Who Stare at Goats with $13.3 million (£8.3 million).
U.F.O. thriller Fourth Kind and horror Paranormal Activity round out the top five.
As Unidentified Flying Objects (UFOs) are perceived as a threat to the safety of Earth, governments unite and sponsor the construction of SHADO (Supreme Headquarters, Alien Defense Organization). Closely guarded under a veil of deep secrecy, it is housed beneath the Harlington-Straker film studios in London. Establishing bases on both the Earth and the Moon, and incorporating highly complex defense equipment, SHADO's battle against alien invaders (kept secret for fear of causing widespread panic) is dramatized as it attempts to discover who they are, where they come from, and what they want.